Nickel silicide is a desired target as a conductive layer within a semiconductor device. However, working with nickel silicide is difficult as etching nickel silicide may produce non-volatile reactive by-products, depending upon the reaction conditions. The presence of non-volatile reactive by-products may result in problematic metal re-deposition and/or be detrimental to the profile, function, or patterning of a feature disposed within a semiconductor device.
One process useful in the continuous scaling down of features is an atomic layer etch during plasma processing of a substrate. Conventionally, the atomic layer etch is performed using a processing scheme which relies on switching gas mixtures to achieve the appropriate plasma chemical composition for passivation (functionalization, adsorption, deposition) and the appropriate plasma chemical composition for a subsequent etch process.
Typically, a substrate is first exposed to a minimally etching plasma to passivate an upper layer. During the passivation process, the ion energies of the plasma may be less than the threshold for etching the passivated top layer. Next, the passivated layer is exposed to an etching plasma to remove the passivated top layer. However, the inventors have observed such a scheme suffers, especially where the layer to be etched is nickel silicide, from the formation of problematic plasma generated particulate by-products including non-volatile by-products and/or insoluble by-products including metal and metallic compounds. In the case of plasma etching a nickel silicide layer, the metal and metallic compounds problematically redeposit on a workpiece leading to e.g., electrical shorts and other defects such as patterning defects. Some defects include re-deposition of metals and metallic compounds disposed for example on the sidewall of a feature disposed upon a workpiece which may be detrimental to a feature sidewall profile, resulting in non-straight feature profiles which are problematic for downstream processing.
Accordingly, the inventor has developed improved methods of processing a substrate and etching a nickel silicide layer.